1. Field of the Invention
This invention relates generally to a phased array antenna including a plurality of spiral arm antenna elements and, more particularly, to a phased array antenna including a plurality of hexagonal shaped, spiral arm antenna elements arranged in concentric rings, where the ends of the arms of diagonally adjacent antenna elements are positioned relative to each other to provide element-to-element coupling to increase the antennas bandwidth.
2. Discussion of the Related Art
Modern tactical military aircraft require radio communications over several frequency bandwidths and communication modes to support the communications, navigation and identification (CNI) functions necessary for operation of the aircraft. These radio frequency (RF) bandwidths generally include the VHF frequency modulation (FM) band (30-88 MHz), the VHF amplitude modulation (AM) band (118-174 MHz) and the UHF band (225-400 MHz). These aircraft also typically include satellite communications systems that support military command, control, communications and intelligence (C3I) functions. These satellite communications signals typically are in the 1-20 GHz frequency range (X, Ku, L-bands).
Suitable antenna systems are necessary to support the various CNI and C3I functions on the aircraft over the several frequency bands of interest. For the high frequency satellite communications functions, a low cost, wideband antenna that supports a plurality of high frequency, circularly-polarized antenna beams is necessary. Common gimbaled, parabolic dish antennas are sufficient to support most of the satellite communications functions for the antenna beams at these frequencies. Such dish antennas are known to be mounted on aircraft, or other vehicles, at a suitable location where a large radome is used to cover the parabolic dish.
The known dish antennas for satellite communications functions have a number of drawbacks when used in military applications, particularly on aircraft. These drawbacks include the fact that a dish antenna is generally limited to only receiving and/or transmitting one antenna beam at any given time. Thus, multiple high gain dish antennas are necessary to support the several satellite communications frequencies. Additionally, wideband circularly-polarized dish antenna feeds are very costly and suffer from poor RF performance. More importantly, modern warfare surface ships, aircraft, and command and control vehicles must have a low radar cross section (RCS), or radar signature, to survive in hostile warfare environments. One or more dish antennas mounted on an aircraft or other military vehicle significantly increases the RCS of the vehicle, making the use of the non-conformal dish antennas undesirable in the warfare environment.
What is needed is a suitable satellite communications antenna for use on military vehicles that is low cost, has a wide bandwidth, simultaneously supports a plurality of antenna beams, and has a low RCS. It is therefore an object of the present invention to provide such an antenna system.